Canola, corn and vegetable oils as alternative for wheat germ oil in fruit fly liquid larval diets

Authors: Chang, Chiou; AFUOLA, FASIA - University Of Hawaii; XIAO LI, QING - University Of Hawaii

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2009
Publication Date: 3/1/2011
Citation: Chang, C.L., Afuola, F., Xiao Li, Q. 2011. Canola, corn and vegetable oils as alternative for wheat germ oil in fruit fly liquid larval diets. Journal of Applied Entomology. 161-167.

Interpretive Summary: The Sterile Insect Technique (SIT) was a first genetics approach of pest control and was developed to suppress fruit fly population worldwide. This technique requires males to be exposed to gamma rays, which damage the chromosomes in the sperm, to induce sexual sterility and then release them into target population. When the released sterile males mate with wild females, the eggs of wild females are fertilized with sperms from irradiated males, cell division is disrupted, and the embryo dies. If sufficient numbers of sterile males are released into the wild over several generations, the reproductive success of the wild population can be progressively reduced and extinguished. As the SIT relies upon efficient competition of released sterile male insects with wild males to mate with wild females, one of the most important components in the process for suppression of fruit fly population is to have a well-established rearing diet and methodology to mass rear quality fruit flies. USDA-ARS recently developed a cost effective liquid diet for mass rearing fruit fly larvae to support the SIT Program. The fruit fly quality from larvae reared with this liquid diet has been satisfactory. This liquid diet technology has been transferring to more than 36 interested groups with more than 26 species of fruit flies or other insects worldwide for evaluation and has been onsite demonstrated in three medfly mass rearing facilities including the world’s largest EL Pino medfly mass rearing facilities in Guatemala and Valencia, Spain. One of the hindered factors for implementing liquid diet technology has been lack of resources of wheat germ oil due to either high cost or availability in locality. Wheat germ oil is an indispensible ingredient in the fruity fly liquid larval rearing diet. The significance of wheat germ oil in the liquid larval diet is to provide the necessary nutrients and fatty acids essential for normal larval development and reproduction. However, it is very difficult to obtain wheat germ oil in numerous countries. Wheat germ oil costs approximately $96 per gallon (3.8 liters). One gallon of wheat germ oil can be prepared for 400 trays based on the formulation of Chang et al. (2006, 2007). It costs $0.24 per tray. With other oils such as corn oil, vegetable oil, canola oil, they cost approximately $0.05 per tray. Our objective is to find an economical and readily available alternative to replace wheat germ oil as a fruit fly larval diet ingredient to rear quality fruit flies to achieve the cost-effective SIT goal.

Technical Abstract: Four wheat germ oil alternatives (corn oil, vegetable oil, canola oil with 10% vitamin E, and canola oil with 20% vitamin E) purchased from a Hawaii local supermarket were added into a fruit fly liquid larval diet as a supplement for rearing fruit fly larvae and were evaluated for the possibility to replace the wheat germ oil based on pupal recovery (%), larval duration (d), pupal weight (mg), adult emergence (%), adult fliers (%), mating (%), egg production per female per day, egg hatch (%), and peak egging period (d) on three species of fruit flies in Hawaii, Ceratitis capitata (TSL strain), Bactrocera dorsalis, and B. cucurbitae. Diets with wheat germ oil and without any oil were used as controls. Our intention is to select the best performance and cost effective alternative oils to replace the currently used pricy and “hard-to-find” wheat germ oil. The results showed that wheat germ oil can be substituted with corn oil, vegetable oil, or canola oils for B. cucurbitae while corn oil is a better alternative for B. dorsalis and vegetable oil is the best for C. capitata to substitute wheat germ oil.